Multimeter Tutorial Includes:
Test meter basics Analogue multimeter DMM digital multimeter How a DMM works DMM accuracy & resolution How to buy best digital multimeter How to use a multimeter Voltage measurement Current measurements Resistance measurements Diode & transistor test Fault finding transistor circuits
Multimeters are very cheap to buy and are one of the most commonly used pieces of electronics test equipment. Although basic operational multimeter instruction may be given when the test meter is bought, details of how to use the multimeter to test circuits and gain the maximum use from them are not always available.
Although there are major differences between the internal circuits within analogue and digital multimeters, the way in which they are used is comparatively similar. However separate sections are given below with instructions on how to use a digital multimeter and how to use an analogue multimeter.
How to use a digital multimeter
When looking at how to use a digital multimeter, DMM, it is worth understanding the main controls.
Normally towards the top of the main front panel is a screen which gives the readings and possibly a few other indications.
There will also be a main switch to select the measurement type: amps, volts, ohms, and any other types of measurement that need to be made. This may include an off position, although some meters include a separate on / off switch.
There will also be the connections for the probes. Years ago, these connectors were usually normal banana type plugs, but with safety more prominent these days, similar connectors, but with more protection against accidental touching of the conductive surfaces.
There are normally three or possibly four connections. One is a common connection to which the black probe is normally taken. another is typically for measuring voltage and resistance. The third is typically for current measurements, and there may even be one for low current ranges.
There may be additional connections for temperature probes or for transistor tests where three connections are needed, etc
The operation of a DMM, digital multimeter, itself is normally very straightforward. With a knowledge of how to make voltage, current and resistance measurements, it is then a matter of putting the multimeter to use. If the meter is new then it will obviously be necessary to install a battery to power it. This is normally simple and straightforward and details can be found in the operating instructions for the DMM.
... apart from amps, volts, and ohms, many DMMs can measure parameters including frequency, capacitance, continuity, and temperature....
Using a digital multimeter is quite straightforward - some simple steps enable them to be used easily.
When using the meter it is possible to follow a number of simple steps:
- Turn the meter on
- Insert the probes into the correct connections - this is required because there may be a number of different connections that can be used.
- Set switch to the correct measurement type and range for the measurement to be made. When selecting the range, ensure that the maximum range is above that anticipated. The range on the DMM can then be reduced as necessary. However by selecting a range that is too high, it prevents the meter being overloaded.
- Optimise the range for the best reading. If possible enable all the leading digits to not read zero, and in this way the greatest number of significant digits can be read.
- Once the reading is complete, it is a wise precaution to place the probes into the voltage measurement sockets and turn the range to maximum voltage. In this way if the meter is accidentally connected without thought for the range used, there is little chance of damage to the meter. This may not be true if it left set for a current reading, and the meter is accidentally connected across a high voltage point!
How to use an analogue multimeter
The operation of an analogue multimeter is quite easy. With a knowledge of how to make voltage, current and resistance measurements it is only necessary to know how to use the multimeter itself.
Typically the analogue test meter will have the main meter dial, and below this there will be a switch for the range. Normally only one switch is used, but on occasions more than one is used as in the case of the British AVO 8.
The switch will have positions for DC and AC voltage as well as DC and AC current. There will also be ranges for resistance.
As for the digital multimeter, there will be different connections for the test probes. Often the protection fo these connections is not as rigorous as for the digital multimeters - many analogue meters are much older and may not have the same safety standards when they were made. Accordingly extra care is needed when handling them.
If the meter is new then it will obviously be necessary to install any battery or batteries needed for the resistance measurements.
... analogue multimeters have been available for many years and they are very flexible in their operation....
Using an analogue multimeter is just as easy as using a digital one, but a few differences will be seen.
When using the meter it is possible to follow a number of simple steps:
- Insert the probes into the correct connections - this is required because there may be a number of different connections that can be used. Be sure to get the right connections, and not put them into the ones for a low current measurement if a high voltage measurement is to be made - this could damage the multimeter.
- Set switch to the correct measurement type and range for the measurement to be made. When selecting the range, ensure that the maximum for the particular range chosen is above that anticipated. The range on the multimeter can be reduced later if necessary. However by selecting a range that is too high, it prevents the meter being overloaded and any possible damage to the movement of the meter itself.
- Optimise the range for the best reading. If possible adjust it so that the maximum deflection of the meter can be gained. In this way the most accurate reading will be gained.
- Once the reading is complete, it is a wise precaution to place the probes into the voltage measurement sockets and turn the range to maximum voltage position. In this way if the meter is accidentally connected without thought for the range to be used, there is little chance of damage to the meter. This may not be true if it left set for a current reading, and the meter is accidentally connected across a high voltage point!
General hints and tips
Regardless of the type of test meter used, whether an analogue of digital multimeter, DMM, there are several points that are worth remembering:
- Care when handling probes: Although the probes have been designed for probing points on a circuit, it is still easy for them to slip. Occasionally this can cause a short circuit, so care is required when probing, making sure that the probes do not slip.
- Turn meter off when not in use: When the test meter is not in use, it is always wise to turn it off. Although analogue meters do not have an on/off button, digital ones do and they will use up battery power when they are on. Some will have an auto-off capability but not all will. It is always wise to turn a DMM off when not in use. In this way the battery is less likely to go flat and be ready for use when it is needed.
- Return meter to high voltage switch position after use: When using a test meter, either analogue or digital it is wise to return the range switch to the highest voltage position after use. In this way, if the test meter is used without being set to the correct range, as can easily happen when involved in testing, no damage will result. If it was set to a low current range, there could be a distinct possibility of damage, if for example, it was intended to measure a large voltage.
- Get the polarity right for analogue test meters: If the sense of the voltage or current is incorrect for an analogue test meter, the meter needle will deflect backwards, and if a large reading is present, this could damage the meter movement. It is always wise to ensure that the expected reading is in the correct sense for the way the circuit is being probed.
- Select highest range for first measurement: It is important for any meter, and especially analogue test meters that the highest range is selected first. In this way if a large voltage is present the meter will not be overloaded. Some digital multimeters have a capability known as auto-ranging where it selects the range once it has been set to current voltage of resistance, etc, but for others the range as well as measurement type needs to be set. This can be very important for analogue test meters as the meter movement can be damaged if it is overloaded too much.
These are just a few general hints and tips to help in the use of multimeters, both analogue and digital.
More in depth understanding of measurements
The main measurements to be made using test meters are those of voltage, current and resistance. The voltage measurements are the most straightforward, but current and resistance should also not present any major issues. Further details are given in the links below.
- Voltage measurements: Voltage measurements are typically by selecting the right range, and then placing the probes across the two points to be measured. Normally the black probe is used for connecting to ground, and the red one of the higher voltage.
Read more about . . . . voltage measurements with a test meter.
- Current measurements: When making current measurements using a test meter it is normally necessary to make a break in the circuit and place the meter in line with the circuit so that the current flows through the meter. In this way it measures the current. Although there are ways where the circuit does not have to be broken, tis is the most widely used method.
Read more about . . . . current measurements using a test meter.
- Resistance measurements: Resistance measurements are easy to make with both analogue and digital multimeters. The measurements can simply be made by placing the resistor across the two probes and measuring the resistance. Selecting the most appropriate range is obviously key. When making a resistance measurement, this is best done with the component removed from the circuit otherwise other circuit components will affect the result. Also capacitors will take time to charge up and this will mean a final reading is not achieved for a while. Also diodes will give different values in the different directions.
Read more about . . . . resistance measurements with a test meter.
Analogue test meters can generally only make measurements of current, voltage, and resistance - AC and DC ranges are normally available for both current and voltage.
Digital multimeters can make these measurements and in addition to this, many DMMs can also make measurements of capacitance, frequency, perform diode and transistor tests, some may be able to make temperature measurements and there are even other measurements that can be made. Check the instructions fo the DMM as to exactly what can be done and the ways on which the tests can be undertaken.
Multimeters are very easy to use, and they are the most essential piece of test equipment that is needed if any electronics construction work is to be undertaken. Fortunately the multimeter instructions of how to use them are straightforward, and they should give many years of good service is treated well. Additionally it is possible to use a multimeter to perform many types of test. Even the older analogue meters can be used in a variety of ways, and digital multimeters often have many measurement capabilities beyond the basic amps volts and ohms measurements.
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